Thermal Energy Conversion Method

ABSTRACT

A method for converting thermal energy into mechanical energy in a thermodynamic cycle includes placing a thermal energy source in thermal communication with a heat exchanger arranged in a working fluid circuit containing a working fluid (e.g., sc-CO2) and having a high pressure side and a low pressure side. The method also includes regulating an amount of working fluid within the working fluid circuit via a mass management system having a working fluid vessel, pumping the working fluid through the working fluid circuit, and expanding the working fluid to generate mechanical energy. The method further includes directing the working fluid away from the expander through the working fluid circuit, controlling a flow of the working fluid in a supercritical state from the high pressure side to the working fluid vessel, and controlling a flow of the working fluid from the working fluid vessel to the low pressure side.

RELATED APPLICATIONS

The present application is a continuation of U.S. Utility PatentApplication having Ser. No. 12/631,400, which was filed Dec. 4, 2009,and which claims priority to U.S. Provisional Patent Application havingSer. No. 61/243,200, which was filed Sep. 17, 2009. These priorityapplications are incorporated herein in their entirety, to the extentconsistent with the present application.

FIELD OF THE INVENTION

The present invention is in the field of thermodynamics and is morespecifically directed to a heat engine and a related heat to electricitysystem that utilizes the Rankine thermodynamic cycle in combination withselected working fluids to produce power from a wide range of thermalsources.

BACKGROUND OF THE INVENTION

Heat is often created as a byproduct of industrial processes whereflowing streams of liquids, solids or gasses that contain heat must beexhausted into the environment or removed in some way in an effort tomaintain the operating temperatures of the industrial process equipment.Sometimes the industrial process can use heat exchanger devices tocapture the heat and recycle it back into the process via other processstreams. Other times it is not feasible to capture and recycle this heatbecause it is either too high in temperature or it may containinsufficient mass flow. This heat is referred to as “waste” heat. Wasteheat is typically discharged directly into the environment or indirectlythrough a cooling medium, such as water.

Waste heat can be utilized by turbine generator systems which employ awell-known thermodynamic method known as the Rankine cycle to convertheat into work. Typically, this method is steam-based, wherein the wasteheat is used to raise steam in a boiler to drive a turbine. Thesteam-based Rankine cycle is not always practical because it requiresheat source streams that are relatively high in temperature (600.degree.For higher) or arc large in overall heat content. The complexity ofboiling water at multiple pressures/temperatures to capture heat atmultiple temperature levels as the heat source stream is cooled, iscostly in both equipment cost and operating labor. The steam-basedRankine cycle is not a realistic option for streams of small flow rateand/or low temperature.

There exists a need in the art for a system that can efficiently andeffectively produce power from not only waste heat but also from a widerange of thermal sources.

SUMMARY OF THE INVENTION

A waste heat recovery system executes a thermodynamic cycle using aworking fluid in a working fluid circuit which has a high pressure sideand a low pressure side. Components of the system in the working fluidcircuit include a waste heat exchanger in thermal communication with awaste heat source also connected to the working fluid circuit, wherebythermal energy is transferred from the waste heat source to the workingfluid in the working fluid circuit, an expander located between the highpressure side and the low pressure side of the working fluid circuit,the expander operative to convert a pressure/enthalpy drop in theworking fluid to mechanical energy, a recuperator in the working fluidcircuit operative to transfer thermal energy between the high pressureside and the low pressure side of the working fluid circuit, a cooler inthermal communication with the low pressure side of the working fluidcircuit operative to control temperature of the working fluid in the lowside of the working fluid circuit, a pump in the working fluid circuitand connected to the low pressure side and to the high pressure side ofthe working fluid circuit and operative to move the working fluidthrough the working fluid circuit, and a mass management systemconnected to the working fluid circuit, the mass management systemhaving a working fluid vessel connected to the low pressure side of theworking fluid circuit.

In one embodiment, a waste heat energy recovery and conversion deviceincludes a working fluid circuit having conduit and components forcontaining and directing flow of a working fluid between components ofthe device operative to convert thermal energy into mechanical energy,the working fluid circuit having a high pressure side and a low pressureside; a support structure for supporting the conduit of the workingfluid circuit and the components, the components comprising: an expanderoperative to convert a pressure drop in the working fluid to mechanicalenergy, a power generator (such as for example an alternator) which iscoupled to the expander, a recuperator, a cooler, a pump and a pumpmotor operative to power the pump; and a mass management system having amass control tank for receiving and holding the working fluid, the masscontrol tank connected by conduit to the high pressure side of theworking fluid circuit and to the low pressure side of the working fluidcircuit. An enclosure may also be provided to substantially enclose someor all of the components of the device. One or more heat exchangers maybe located on or off of the support structure. The heat exchanger(s),recuperator and cooler/condenser may include printed circuit heatexchange panels. A control system for controlling operation of thedevice may be remote or physically packaged with the device.

The disclosure and related inventions further includes a method ofconverting thermal energy into mechanical energy by use of a workingfluid in a closed loop thermodynamic cycle contained in a working fluidcircuit having components interconnected by conduit, the componentsincluding at least one heat exchanger operative to transfer thermalenergy to the working fluid, at least one expansion device operative toconvert thermal energy from the working fluid to mechanical energy, atleast one pump operative to transfer working fluid through the workingfluid circuit, the working fluid circuit having a high pressure side anda low pressure side, and a mass management system comprising a massmanagement vessel connected by conduit to the low pressure side of theworking fluid circuit, the method including the steps of: placing athermal energy source in thermal communication with a heat exchangercomponent; pumping the working fluid through the working fluid circuitby operation of the pump to supply working fluid in a supercritical orsubcritical state to the expander; directing the working fluid away fromthe expander in a sub-critical state through the working fluid circuitand to the pump; controlling flow of the working fluid in asuper-critical state from the high pressure side of the working fluidcircuit to the mass management vessel, and controlling an amount ofworking fluid in a sub-critical or super-critical state from the massmanagement vessel to the low pressure side of the working fluid circuitand to the pump.

The disclosure and related inventions further includes a mass managementsystem for controlling an amount of working fluid mass in athermodynamic cycle in a working fluid circuit having a pump or acompressor, the mass management system having a working fluid controltank for bolding an amount of the working fluid at a first pressure P,the working fluid control tank located outside of the working fluidcircuit; and a fluid connection between the working fluid control tankand a low pressure side of the thermodynamic cycle in the working fluidcircuit to allow passage of the working fluid between the working fluidcircuit and the working fluid control tank.

These and other aspects of the disclosure and related inventions arefurther described below in representative forms with reference to theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of the heat to electricity system of thepresent invention.

FIGS. 1B-1D illustrate various conduit arrangements and working fluidflow directions in the working fluid circuit.

FIG. 2 is a pressure-enthalpy diagram for carbon dioxide.

FIGS. 3A-3M are schematic drawings of a representative embodiment of aheat engine device and heat engine skid of the present disclosure andrelated inventions.

FIG. 4A is a flow chart of operational states of a heat engine of thedisclosure.

FIG. 4B is a flow chart representing a representative start-up andoperation sequence for a heat engine of the disclosure.

FIG. 4C is a flow chart representing a shut-down sequence for a heatengine of the disclosure.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATE EMBODIMENTS

The inventive heat engine 100 (also referred to herein in thealternative as a “thermal engine”, “power generation device”, “wasteheat recovery system” and “heat recovery system”, “heat to electricitysystem”) of the present disclosure utilizes a thermodynamic cycle whichhas elements of the Rankine thermodynamic cycle in combination withselected working fluid(s), such as carbon dioxide, to produce power froma wide range of thermal sources. By “thermal engine” or “heat engine”what is generally referred to is the equipment set that executes thethermodynamic cycle described herein; by “heat recovery system” what isgenerally referred to is the thermal engine in cooperation with otherequipment to deliver heat (from any source) to and remove heat from theinventive thermal engine.

The thermodynamic cycle executed by the heat engine 100 is describedwith reference to a pressure-enthalpy diagram for a selected workingfluid, FIG. 2. The thermodynamic cycle is designed to operate as aclosed loop thermodynamic cycle in a working fluid circuit having a flowpath defined by conduit which interconnects components of the workingfluid circuit. The thermal engine which operates the cycle may or maynot be hermetically or otherwise entirely sealed (such that no amount ofworking fluid is leaked from the system into the surroundingenvironment).

The thermodynamic cycle that is executed by the thermal engine is shownin its most rudimentary form in FIG. 2 which is a pressure-enthalpydiagram for carbon dioxide. The thermodynamic cycle may be described forease of understanding by referencing a working fluid at point A on thisdiagram. At this point, the working fluid has its lowest pressure andlowest enthalpy relative to its state at any other point during thecycle and as shown on the diagram. From there, the working fluid iscompressed and/or pumped to a higher pressure (point B on the diagram).From there, thermal energy is introduced to the working fluid which bothincreases the temperature of the working fluid and increases theenthalpy of the working fluid (point C on the diagram). The workingfluid is then expanded through a mechanical process to point (D). Fromthere, the working fluid discharges heat, dropping in both temperatureand enthalpy, until it returns to point (A). Each process (i.e., A-B,B-C, C-D, D-A) need not occur as shown on the exemplary diagram and oneof ordinary skill in the art would recognize that each step of the cyclecould be achieved in a variety of ways and/or that it is possible toachieve a variety of different coordinates on the diagram. Similarly,each point on the diagram may vary dynamically over time as variableswithin and external to the system change, i.e., ambient temperature,waste heat temperature, amount of mass in the system.

In the preferred embodiment of the thermal engine, the cycle is executedduring normal, steady state operation such that the low pressure side ofthe system (points A and D on FIG. 2) is between 400 psia and 1500 psiaand the high pressure side of the system is between 2500 psia and 4500psia (points B and C FIG. 2). One of ordinary skill in the art wouldrecognize that either or both higher or lower pressures could beselected for each or all points. In the preferred embodiment of thecycle, it will be observed that between points C and D, the workingfluid transitions from a supercritical state to a subcritical state(i.e., a transcritical cycle); one of ordinary skill in the art wouldrecognize that the pressures at points C and D could be selected suchthat the working fluid remained in a supercritical state during theentire cycle.

In a preferred embodiment of the thermal engine, the working fluid iscarbon dioxide. The use of the term carbon dioxide is not intended to belimited to carbon dioxide of any particular type, purity or grade ofcarbon dioxide although industrial grade carbon dioxide is the preferredworking fluid. Carbon dioxide is a greenhouse friendly and neutralworking fluid that offers benefits such as non-toxicity,non-flammability, easy availability, low price, and no need ofrecycling.

In the preferred embodiment, the working fluid is in a supercriticalstate over certain portions of the system (the “high pressure side”),and in a subcritical state at other portions of the system (the “lowpressure side”). In other embodiments, the entire cycle may be operatedsuch that the working fluid is in a supercritical or subcritical stateduring the entire execution of the cycle.

In various embodiments, the working fluid may a binary, ternary or otherworking fluid blend. The working fluid combination would be selected forthe unique attributes possessed by the fluid combination within a heatrecovery system as described herein. For example, one such fluidcombination is comprised of a liquid absorbent and carbon dioxideenabling the combined fluid to be pumped in a liquid state to highpressure with less energy input than required to compress CO.sub.2. Inanother embodiment, the working fluid may be a combination of carbondioxide and one or more other miscible fluids. In other embodiments, theworking fluid may be a combination of carbon dioxide and propane, orcarbon dioxide and ammonia.

One of ordinary skill in the art would recognize that using the term“working fluid” is not intended to limit the state or phase of matterthat the working fluid is in. In other words, the working fluid may bein a fluid phase, a gas phase, a supercritical phase, a subcriticalstate or any other phase or state at any one or more points within thecycle.

The inventive heat to electricity system may utilize other fluids inother parts of the system, such as water, thermal oils or suitablerefrigerants; these other fluids may be used within heat exchangers andequipment external to the heat engine 100 (such as at the Cooler 12and/or Waste Heat Exchanger 5 shown in FIG. 1A) and within cooling orother cycles and subsystems that operate within the heat to electricitysystem (for example at the Radiator 4 cooling loop provided at thealternator 2 of the thermal engine shown in FIG. 1A).

As further described, in one representative embodiment, a 250 kW (net)or greater skid-based system, as illustrated conceptually in FIGS.3A-3M, is provided for deployment at any source or site of waste orby-product heat. Nominal rated output (electrical or work) is notintended to be a limiting feature of the disclosure or relatedinventions.

The heat engine 100 of the disclosure has three primary classes ofequipment through which the working fluid may be circulated as thethermodynamic cycle is executed, (i) one or more heat exchangers (ii)one or more pumps and/or compressors and (iii) one or more expansion(work) devices (such as a turbine, a ramjet, or a positive displacementexpander 3 such as a geroler or gerotor). Each of these pieces ofequipment is operatively coupled in the cycle as shown on FIG. 1Athrough the use of suitable conduits, couplings and fittings, forexample in a working fluid circuit, as further described.

The heat engine 100 may also include a means for converting mechanicalenergy from the one or more expansion devices into electricity; suchmeans may include but are not limited to a generator, alternator 2, orother device(s) and related power conditioning or conversion equipmentor devices.

In one embodiment, certain components of the heat engine 100 may sharecommon elements such as in the case of a turboalternator (shown on FIG.1A) (where an expansion device shares a common shaft with an alternator2) or in the case of a turbopump, where an expansion device shares acommon shaft with a pump. Alternatively, the expansion device may bemechanically coupled to the electrical generating means (i) bymagnetically coupling the turbine shaft to the rotor of the electricalgenerating means and/or (ii) by a gearbox operatively coupling theturbine shaft and the rotor of the electrical generating means.

The heat engine 100 may also include other equipment and instrumentssuch as sensors, valves (which may be on/off or variable), fittings,filters, motors, vents, pressure relief equipment, strainers, suitableconduit, and other equipment and sensors. The preferred heat engine 100includes the additional equipment shown on FIG. 1A.

The preferred heat engine 100 also includes a system for managing theamount of working fluid within the system such as the mass managementsystem disclosed on FIG. 1A, as further described.

The preferred heat engine 100 also includes a control system and relatedequipment allowing for the automated and/or semi-automated operation ofthe engine, the remote control of the system and/or the monitoring ofsystem performance.

The preferred heat engine 100 also includes one or more cooling cyclesystems to remove heat from and/or provide thermal management to one ormore of the expansion device, the electrical producing means and/or thepower electronics 1. In the preferred embodiment, there is provided acooling cycle shown on FIG. 1A that removes heat from and providesthermal management to the mechanical coupling between the expander 3 andthe alternator 2, the alternator 2, and the power electronics 1.

The system of the current invention is flexible and may utilize manydifferent types of conventional heat exchangers. The preferredembodiment of the inventive heat engine system 100 utilizes one or moreprinted circuit heat exchangers (PCHE) or other construction of the heatexchanger, recuperator or cooler components, each of which may containone or more cores where each core utilizes microchannel technology.

As used herein and known in the art, “microchannel technology” includes,but is not limited to, heat exchangers that contain one or moremicrochannels, mesochannels, and/or minichannels. As used herein theterms “microchannels,” “mesochannels,” and/or “minichannels” areutilized interchangeably. Additionally, the microchannels, mesochannels,and/or minichannels of the present invention are not limited to any oneparticular size, width and/or length. Any suitable size, width or lengthcan be utilized depending upon a variety of factors. Furthermore, anyorientation of the microchannels, mesochannels, and/or minichannels canbe utilized in conjunction with the various embodiments of the presentinvention.

The expansion device (also referred to herein as an “expander”) may be avalve or it may be a device capable of transforming high temperature andpressure fluid into mechanical energy. The expansion device may have anaxial or radial construction; it may be single or multi-staged. Examplesinclude a geroler, a gerotor, other types of positive displacementdevices such as a pressure swing, a turbine, or any other device capableof transforming a pressure or pressure/enthalpy drop in a working fluidinto mechanical energy.

In a preferred embodiment, the device is a turboalternator wherein theturbine is operatively coupled to the alternator 2 by either (i) sharinga single shaft (the “single shaft design”) or by operatively couplingthe turbine shaft to the alternator 2 rotor (or other shaft) by usinghigh powered magnets to cause two shafts to operate as a single shaft.In the preferred embodiment, the turbine is physically isolated from thealternator 2 in order to minimize windage losses within the alternator2. Thus, in the preferred embodiment, while the turbine is operativelycoupled to the alternator 2, the turbine and alternator 2 do not share acommon housing (or casing). In the single shaft design, the turbinecasing is sealed at the common shaft and thereby isolated from thealternator 2 through the use of suitable shaft seals. In the singleshaft design, suitable shaft seals may be any of the following,labyrinth seal, a double seal, a dynamically pressure balanced seal(sometimes called a floating ring or fluid filled seal), a dry gas sealor any other scaling mechanism. In the magnetic coupling design, noshaft seals are required because it is possible to entirely encase theturbine within its housing thereby achieving the desired isolation fromthe alternator 2.

Among other differentiating attributes of the preferred turboalternatorare its single axis design, its ability to deliver high isentropicefficiency (>70%), that it operates at high rotational speeds (>20 Krpm), that its bearings are either not lubricated during operation orlubricated during operation only by the working fluid, and itscapability of directly coupling a high speed turbine and alternator 2for optimized system (turboalternator) efficiency. In the preferredembodiment, the turboalternator uses air-foil bearings; air foilbearings are selected as the preferred design due because they reduce oreliminate secondary systems and eliminate the requirement forlubrication (which is particularly important when working with thepreferred working fluid, carbon dioxide). However, hydrostatic bearings,aerostatic bearings, magnetic bearings and other bearing types may beused.

The heat engine 100 also provides for the delivery of a portion of theworking fluid into the expander 3 chamber (or housing) for purposes ofcooling one or more parts of the expander 3. In a preferred embodiment,due to the potential need for dynamic pressure balancing within thepreferred heat engine's turboalternator, the selection of the sitewithin the thermal engine from which to obtain this portion of theworking fluid is critical because introduction of the portion of theworking fluid into the turboalternator must not disturb the pressurebalance (and thus stability) of the turboalternator during operation.This is achieved by matching the pressure of the working fluid deliveredinto the turboalternator for purposes of cooling with the pressure ofthe working fluid at the inlet of the turbine; in the preferred heatengine 100, this portion of the working fluid is obtained after theworking fluid passes a valve 25 and a filter F4. The working fluid isthen conditioned to be at the desired temperature and pressure prior tobeing introduced into the turboalternator housing. This portion of theworking fluid exits the turboalternator at the turboalternator outlet. Avariety of turboalternator designs are capable of working within theinventive system and to achieve different performance characteristics

The device for increasing the pressure of the working fluid from pointA-B on FIG. 2 may be a compressor, pump, a ramjet type device or otherequipment capable of increasing the pressure of the selected workingfluid. In a preferred embodiment, the device is a pump 9, as depicted inFIGS. 1A-1D. The pump 9 may be a positive displacement pump, acentrifugal pump or any other type or construction of pump.

The pump 9 may be coupled to a VFD (variable frequency drive) 11 tocontrol speed which in turn can be used to control the mass flow rate ofthe working fluid in the system, and as a consequence of this controlthe high side system pressure. The VFD may be in communication with acontrol system, as further described.

In another embodiment of the inventive thermal engine, the pump 9 may beconstructed such that there is a common shaft (not shown) connecting itwith an expansion device enabling the pump to be driven by themechanical energy generated by expansion of the working fluid (e.g., aturbopump). A turbopump may be employed in place of or to supplement thepump of the preferred embodiment. As noted in the section abovedetailing the turboalternator, the “common shaft” may be achieved byusing a magnetic coupling between the expansion device's shaft and thepump shaft. In one embodiment of the heat engine 100 with a turbopump,there is provided a secondary expansion device (not shown) coupled tothe pump by a common shaft. The secondary expansion device is locatedwithin a stream of fluid which runs parallel to the stream to theprimary system expander 3 and there are two valves on either side of thesecondary expander to regulate flow to the second expander. It should benoted that there need not be a second expander in order to form aturbopump. The common shaft of the turbopump may be shared with thecommon shaft of the primary system expander 3 and/or, in a preferredembodiment, the common shaft of the turboalternator. Similarly, if thesystem uses a secondary expansion device to share a common shaft withthe turbopump, the secondary expansion device need not be located asdescribed above.

The electrical producing means of one embodiment of the thermal engineis a high speed alternator 2 that is operatively coupled to the turbineto form a turboalternator (as described above). The electrical producingmeans may alternatively be any known means of converting mechanicalenergy into electricity including a generator or alternator 2. It may beoperatively coupled to the primary system expander 3 by a gear box, bysharing a common shaft, or by any other mechanical connection.

The electrical producing means is operatively connected to powerelectronics 1 equipment set. In the preferred embodiment, the electricaloutput of the alternator 2 is mated with a high efficiency powerelectronics 1 equipment set that has equipment to provide active loadadjustment capability (0-100%). In the preferred embodiment, the powerelectronics 1 system has equipment to provide the capability to converthigh frequency, high voltage power to grid-tie quality power atappropriate conditions with low total harmonic distortion (THD), SAGsupport, current and voltage following, VAR compensation, for providingtorque to start the turboalternator, and dynamic braking capability forversatile and safe control of the turboalternator in the event of loadloss; it has also capability of synchronizing and exporting power to thegrid for a wide voltage and speed range of the alternator 2.

In the preferred embodiment, the pump 9 inlet pressure has a directinfluence on the overall system efficiency and the amount of power thatcan be generated. Because of the thermo-physical properties of thepreferred working fluid, carbon dioxide, as the pump 9 inlet temperaturerises and falls the system must control the inlet pressure over wideranges of inlet pressure and temperature (for example, from −4 degreesF. to 104 degrees F.; and 479 psia to 1334 psia). In addition, if theinlet pressure is not carefully controlled, pump 9 cavitation ispossible.

A mass management system is provided to control the inlet pressure atthe pump 9 by adding and removing mass from the system, and this in turnmakes the system more efficient. In the preferred embodiment, the massmanagement system operates with the system semi-passively. The systemuses sensors to monitor pressures and temperatures within the highpressure side (from pump 9 outlet to expander 3 inlet) and low pressureside (from expander 3 outlet to pump 9 inlet) of the system. The massmanagement system may also include valves, tank heaters or otherequipment to facilitate the movement of the working fluid into and outof the system and a mass control tank 7 for storage of working fluid.

As shown on FIG. 1A, in the case of the preferred embodiment, the massmanagement system includes the equipment operatively connected by thebolded lines or conduits of the diagram and at (and including) equipmentat the termination points of the mass control system (e.g., 14, 15, 16,17, 18, 21, 22, and 23). The preferred mass management system removeshigher pressure, denser working fluid (relative to the pressure,temperature, and density on the low pressure side of the system) fromthe thermodynamic cycle being executed by the thermal engine via valve16. The mass management system dispenses working fluid into the mainheat engine system 100 via valves 14 and 15. By controlling theoperation of the valves 14, 15 and 16, the mass management system addsor removes mass from the system without a pump, reducing system cost,complexity and maintenance.

As further shown in FIGS. 1B-1D, the Mass Control Tank 7 is filled withworking fluid. It is in fluid communication with valves 14 and 16 suchthat opening either or both valves 14, 16 will deliver working fluid tothe top of the Mass Control Tank 7. The Mass Control Tank 7 is in fluidcommunication with valve 15 such that opening valve 15 will removeworking fluid from the bottom of the Mass Control Tank 7. The workingfluid contained within the Mass Control Tank 7 will stratify with thehigher density working fluid at the bottom of the tank and the lowerdensity working fluid at the top of the tank. The working fluid may bein liquid phase, vapor phase or both; if the working fluid is in bothvapor phase and liquid phase, there will be a phase boundary separatingone phase of working fluid from the other with the denser working fluidat the bottom of the Mass Control Tank 7. In this way, valve 15 willalso deliver to the system the densest working fluid within the MassControl Tank 7.

In the case of the preferred embodiment, this equipment set is combinedwith a set of sensors within the main heat engine system 100 and acontrol system as described within.

In the case of the preferred embodiment, this mass management systemalso includes equipment used in a variety of operating conditions suchas startup, charging, shut-down and venting the heat engine system 100as shown on FIG. 1A.

Exemplary operation of the preferred embodiment of the mass managementsystem follows. When the working fluid in the mass control tank 7 is atvapor pressure for a given ambient temperature, and the low sidepressure in the system is above the vapor pressure, the pressure in themass control tank 7 must be increased, to allow for the addition of massinto the system. This can be controlled by opening the valve 14 andthereby allowing higher pressure, higher temperature, lower densitysupercritical working fluid to flow into the mass control tank 7. Valve15 is opened to allow higher density liquid working fluid at the bottomof the mass control tank 7 to flow into the system and increase pumpsuction pressure.

The working fluid may be in liquid phase, vapor phase or both. If theworking fluid is in both vapor phase and liquid phase, there will be aphase boundary in the mass control tank 7. In general, the mass controltank 7 will contain either a mixture of liquid and vapor phase workingfluid, or a mass of supercritical fluid. In the former case, there willbe a phase boundary. In the latter case, there will not be a phaseboundary (because one does not exist for supercritical fluids). Thefluid will still tend to stratify however, and the valve 15 can beopened to allow higher density liquid working fluid at the bottom of themass control tank 7 to flow into the system and increase pump suctionpressure. Working fluid mass may be added to or removed from the workingfluid circuit via the mass control tank 7.

The mass management system of the disclosure may be coupled to a controlsystem such that the control of the various valves and other equipmentis automated or semi-automated and reacts to system performance dataobtained via sensors located throughout the system, and to ambient andenvironmental conditions.

As shown in FIGS. 1B-1D, other configurations for controlling pressureand/or temperature (or both) in the mass control tank 7 in order to movemass in and out of the system (i.e., the working fluid circuit), includethe use of a heater and/or a coil 32 within the vessel/tank 7 or anyother means to add or remove heat from the fluid/vapor within the masscontrol tank 7. Alternatively, mechanical means, such as providing pumpmay be used to get working fluid from the mass control tank 7 into thesystem.

One method of controlling the pressure of the working fluid in the lowside of the working fluid circuit is by control of the temperature ofthe working fluid vessel or mass control tank 7. A basic requirement isto maintain the pump 9 inlet pressure above the boiling pressure at thepump 9 inlet. This is accomplished by maintaining the temperature of themass control tank 7 at a higher level than the pump inlet temperature.Exemplary methods of temperature control of the mass control tank 7 are:direct electric heat; a heat exchanger coil 32 with pump 9 dischargefluid (which is at a higher temperature than at the pump 9 inlet), or aheat exchanger coil 32 with spent cooling water from thecooler/condenser (also at a temperature higher than at the pump 9inlet).

As shown in FIGS. 3A-3M, with continuing reference to FIGS. 1A-1D, thewaste heat recovery system of the disclosure may be constructed in oneform with the primary components described and some or all of which maybe arranged on a single skid or platform or in a containment orprotective enclosure, collectively referred to herein as a “skid” or“support structure”. FIGS. 3A-3M illustrate a representative embodimentof the inventive heat engine 100 with exemplary dimensions, portlocations, and access panels. Some of the advantages of the skid typepackaging of the inventive heat engine 100 include general portabilityand installation access at waste heat sources, protection of componentsby the external housing, access for repair and maintenance, and ease ofconnection to the inventive heat engine 100 energy output, to a grid, orto any other sink or consumer of energy produced by the inventive heatengine 100. As shown in FIGS. 3A-3M, the heat engine 100 is constructedupon a frame having the representative and exemplary dimensions, andwithin a housing on the frame. Access and connection points are providedexternal to the housing as indicated, in order to facilitateinstallation, operation and maintenance. FIGS. 3B-3E indicate thevarious operative connections to the inventive heat engine 100 includingthe waste heat source supply 19, cooling water supply 27, and waste heatsource and cooling water return lines 20, 28, respectively (FIG. 3B);instrument air supply 29 and a mass management (working fluid) fillpoint 21 (FIG. 3C); expander 3 air outlet 30 and pressure relief valvesexhaust 22 (FIG. 3D); and CO2 pump vent 30, high pressure side vent 23,and additional pressure relief valve exhaust (FIG. 3E). Adequateventilation, cooling via radiators 4 as required and sound-proofing isalso accommodated by the housing design. The principle components of thesystem are indicated on FIG. 3M and illustrated pipe connections. Thevariable frequency drive (VFD) 11, programmable logic controller (PLC)and electrical power panel (Power Out) are schematically illustrated asinstalled within the housing.

Also included on or off the skid, or otherwise in fluid or thermalcommunication with the working fluid circuit of the system, is at leastone waste heat exchanger (WHE) 5 (also shown in FIG. 1A). The WHE uses aheat transfer fluid (such as may be provided by any suitable workingfluid or gas, such as for example Therminol XP), which is ported to theWHE 5 from an off-skid thermal source, through the exterior of the skidenclosure through a waste heat source supply port 19, through the WHE 5circuit to a waste heat source return 20 exiting the housing (FIGS.3A-3E). In the preferred embodiment, heat is transferred to the systemworking fluid in the waste heat exchanger 5. The working fluid flow andpressure entering the expander EXP 3 may be controlled by the start,shutoff and bypass valves and by the control system provided herein.Also provided is a cooler 12, where additional residual heat within theworking fluid is extracted from the system, increasing the density ofthe working fluid, and exits the cooler 12 and into the System Pump 9.The cooler 12 may be located on or off the skid.

Supercritical working fluid exits the pump 9 and flows to therecuperator (REC) 6, where it is preheated by residual heat from the lowpressure working fluid. The working fluid then travels to the waste heatexchanger (WHE) 5. From WHE 5, the working fluid travels to the expander(EXP) 3. On the downstream side of the EXP 3, the working fluid iscontained in a low pressure side of the cycle. From the EXP 3 theworking fluid travels through the REC 6, then to the cooler 12 and thenback to the Pump 9.

Suitable pressure and temperature monitoring at points along the linesand at the components is provided and may be integrated with anautomated control system.

A control system can be provided in operative connection with theinventive heat engine system 100 to monitor and control the describedoperating parameters, including but not limited to: temperatures,pressures (including port, line and device internal pressures), flowmetering and rates, port control, pump operation via the VFD, fluidlevels, fluid density leak detection, valve status, filter status, ventstatus, energy conversion efficiency, energy output, instrumentation,monitoring and adjustment of operating parameters, alarms and shut-offs.

As further described, a representative control system may include asuitably configured programmable logic controller (PLC) with inputs fromthe described devices, components and sensors and output for control ofthe operating parameters. The control system may be integral with andmounted directly to the inventive heat engine 100 or remote, or as partof distributed control system and integrated with other control systemssuch as for an electrical supply grid. The control system isprogrammable to set, control or change any of the various operatingparameters depending upon the desired performance of the system.Operating instrumentation display may be provided as a compositedashboard screen display of the control system, presenting textual andgraphic data, and a virtual display of the inventive heat engine 100 andoverall and specific status. The control system may further includecapture and storage of heat engine 100 operational history and ranges ofall parameters, with query function and report generation.

A control system and control logic for a 250 kW nominally net powerrated Thermafficient Heat Engine 100 of the disclosure may include thefollowing features, functions and operation: automated unmannedoperation under a dedicated control system; local and remote humanmachine interface capability for data access, data acquisition, unithealth monitoring and operation; controlled start-up, operation and shutdown in the case of a loss of electrical incoming supply power or powerexport connection; fully automated start/stop, alarm, shut down, processadjustment, ambient temperature adjustment, data acquisition andsynchronization; a controls/power management system designed forinterfacing with an external distributed plant control system.

An exemplary control system for the thermafficient heat engine 100 mayhave multiple control states as depicted in FIG. 4A, including thefollowing steps and functions. Initial fill of a working fluid at 41 topurge and fill an empty system allowing system to warm for startup.Top-up fill at 47 to add mass to the mass management tank(s) while thesystem is in operation. Standby at 40 for power up of sensors andcontroller; no fluid circulation; and warm-up systems active ifnecessary. Startup at 42. Recirculation idle at 43 with fluidcirculation with turbine in bypass mode; gradually warming uprecuperator, cooling down waste heat exchanger; BPVVVHX initially open,but closes as hot slug is expelled from waste heat exchanger. Minimumidle at 44, with turbine at minimum speed (.about.20 k RPM) to achievebearing lift-off; Turbine speed maintained (closed-loop) through acombination of pump speed and valve 24 position. Full speed idle at 45,with turbine at design speed (40 k RPM) with no load; Pump speed setsturbine speed (closed-loop). Operation at 46, with turbine operating atdesign speed and produced nominal design power; switch to load controlfrom pump speed control by ramping up pump speed while using powerelectronics 1 load to maintain turbine speed at 40 k RPM. Shutdown at48, with controlled stop of the turboexpander 3 and gradual cooling ofthe system. An emergency shutdown at 49, for unexpected system shutdown;the pump 9 and turboexpander 3 brought down quickly and heat exchangersallowed to cool passively, and, venting at 50 to drain the system andremove pressure for maintenance activities.

As represented in FIG. 4C, other functions of the control system mayinclude an check trips and alarms 51, with control links to shutdown 48and emergency shutdown 49, startup 42, and continued operation with arecoverable alarm state.

The invention thus disclosed in sufficient particularity as to enablingan understanding by those of skill in the art, the following claimsencompassing all of the concepts, principles and embodiments thusdescribed, and all equivalents.

1. A method for controlling inlet pressure of a pump in a closed loopthermodynamic cycle, comprising: circulating a working fluid in aworking fluid circuit that includes the pump fluidly coupled to anexpander that is operative to convert energy from the working fluid intomechanical energy, the working fluid circuit including a high pressureside and a low pressure side; receiving first data corresponding to ameasured pressure at the high pressure side of the working fluidcircuit; receiving second data corresponding to a measured pressure atthe low pressure side of the working fluid circuit; and adding orremoving working fluid mass from the working fluid circuit via a massmanagement system based on the first data, the second data, or acombination thereof, the mass management system being connected to theworking fluid circuit and having a working fluid vessel fluidly coupledto the low pressure side of the working fluid circuit.
 2. The method ofclaim 1, further comprising: receiving third data that corresponds to ameasured temperature at the high pressure side of the working fluidcircuit; and receiving fourth data that corresponds to a measuredtemperature at the low pressure side of the working fluid circuit. 3.The method of claim 2, further comprising determining whether workingfluid mass should be added or removed from the working fluid circuitbased on the third data, the fourth data, or a combination thereof. 4.The method of claim 1, further comprising actuating one or more valvescoupled to the mass management system to add or remove working fluidmass from the working fluid circuit.
 5. The method of claim 4, whereinthe actuation of the one or more valves is automated.
 6. The method ofclaim 1, further comprising filling the working fluid vessel withworking fluid.
 7. The method of claim 1, further comprising receivingworking fluid vessel data that corresponds to a measured pressure in theworking fluid vessel.
 8. The method of claim 7, further comprisingdetermining whether the working fluid vessel data is less than thesecond data that corresponds to the measured pressure at the lowpressure side of the working fluid circuit.
 9. The method of claim 8,further comprising adding supercritical carbon dioxide to the workingfluid vessel and adding working fluid mass into the low pressure side ofthe working fluid circuit from the working fluid vessel if the workingfluid vessel data is less than the second data.
 10. The method of claim1, wherein the working fluid comprises carbon dioxide in a supercriticalstate in the high pressure side.
 11. A method of controlling workingfluid in a working fluid circuit during different stages of operation,comprising: circulating the working fluid in the working fluid circuitthat includes a pump fluidly coupled to an expander that is operative toconvert energy from the working fluid into mechanical energy, theworking fluid circuit including a high pressure side and a low pressureside, and the working fluid circuit further including a mass managementsystem comprising a mass management vessel fluidly connected to the lowpressure side of the working fluid circuit; filling the mass managementvessel with working fluid upon startup of the working fluid circuit; andfilling the working fluid vessel at a top side of the working fluidvessel while the working fluid circuit is in operation.
 12. The methodof claim 11, further comprising halting fluid circulation in the massmanagement vessel prior to startup while sensors positioned in the lowpressure side and the high pressure side are warmed up.
 13. The methodof claim 11, wherein the working fluid comprises carbon dioxide in asupercritical state in the high pressure side.
 14. A method forcontrolling inlet pressure of a pump in a closed loop thermodynamiccycle, comprising: circulating a working fluid in a working fluidcircuit that includes the pump fluidly coupled to an expander that isoperative to convert energy from the working fluid into mechanicalenergy, the working fluid circuit including a high pressure side and alow pressure side, and the working fluid circuit further including amass management system that includes a working fluid vessel fluidlyconnected to the low pressure side of the working fluid circuit;receiving first data corresponding to a measured temperature at the highpressure side of the working fluid circuit; receiving second datacorresponding to a measured temperature at the low pressure side of theworking fluid circuit; receiving third data corresponding to a measuredtemperature in the working fluid vessel of the mass management system;determining whether temperature of the working fluid should be adjustedwithin the working fluid vessel based on the first data, the seconddata, the third data, or a combination thereof; and adjusting thetemperature of the working fluid within the working fluid vessel asnecessary.
 15. The method of claim 14, further comprising maintainingthe temperature of the working fluid in the working fluid vessel at ahigher level than the temperature at the low pressure side of theworking circuit.
 16. The method of claim 15, further comprising using adirect electric heat source to increase the temperature of the workingfluid within the working fluid vessel.
 17. The method of claim 15,further comprising: positioning a heat exchanger coil within the workingfluid vessel; and increasing the temperature of the working fluid withinthe working fluid vessel via the heat exchanger coil.
 18. The method ofclaim 16, further comprising using a controller to automate the directelectric heat source when the temperature of the working fluid in theworking fluid vessel drops below the temperature of the working fluid inthe low pressure side of the working circuit.
 19. The method of claim17, further comprising using a controller to automate the heating of theheat exchanger coil when the temperature of the working fluid in theworking fluid vessel drops below the temperature of the working fluid inthe low pressure side of the working circuit.
 20. The method of claim12, wherein the working fluid comprises carbon dioxide in asupercritical state in the high pressure side.